During 1923, the distinction between various HMV coloured labels for 'celebrity' artists was abolished and most ensembles were given the familiar 'red' labels for which the DB series is instantly recognisable to collectors. It was also the first time that celebrity records were first issued in double-sided format. Nearly all single-sided records that had been previously issued, were paired off and later others, previously deleted, were reissued in this new form. "This represented the last stage in the evolution of the acoustic record." as noted by Semeonoff in his definitive book, 'Record Collecting' , and heralded in a new era for the electrically recorded disc and the rapid expansion of the 'DB' series.
Important milestones in the development of the 'DB' Red Label Series
Boris Semeonoff outlines the development of the DB series very succinctly in his book, Collecting Records; and I urge readers to seek out a copy of this interesting and informative book to explore this subject further; so I'll only briefly outline the key milestones to illustrate the development and changes that occurred in the recording industry and HMV...
1896 - First 'Berliner' records available
1900 - First 'G & T' records appear
1906 - First pink-label Celebrity records issued (The foundation of the 'DB' series)
1908 - 'Pre-Dog' labels appear on the market for the first time
1910 - 'Dog Monarch' (12inch) and 'Dog Concert' (10inch) recordings appear
1912 - The use of the 'His Master's Voice' inscription first used on records
1923 - Elimination of coloured labels for celebrities begins (with some exceptions...)
1924 - First double-sided Celebrity records issued in both the (DB and DA series)
1925 - First electrical recordings issued (DB 853 - Alfred Cortot - Ballade in G/Impromptu in F (Chopin) - Recorded 21 March 1925, Camden, New Jersey) 
1927 - New, streamlined red-label issued (eliminating lower 'corners' of the label)
1933 - Additional changes to the red-label DB series with catalog number below 'Dog' trademark
1934 - Phasing out of separate serial and matrix numbers
The structure of the DB series is worth considering for a moment as it helps the collector understand how the catalog numbers of this series evolved over its lifetime. At first glance, the series may seem sequential, but the fact is, it isn't.
Affiliated branches of HMV were assigned blocks of catalog numbers for the 'DB' series dependant on the country of recording. These numbers were (more or less) sequentially used for each new recording during the 78rpm era. This can be seen by variations in matrix numbers when the whole series is examined as a whole.
As a indirect or direct result of this, there are often gaps of missing numbers which were never assigned to recordings or for various reasons. In some cases, these allotted issues, were rejected on artistic grounds or technical issues or simple never used. This phenomenon is particularly evident, but not exclusive to records around the DB 5700 mark onwards.
The following table outlines the 'sequence' of record numbers as allotted by country. Hence, dating records in the DB series according to catalog numbers (or matrix numbers for that matter) is, as Kelly notes,  "not possible ... in so large a field."
'DB' catalog numbers by country:
- DB 1-20 - Danish Wartime Issues
- DB 100-4049 - 'International' Issues
- DB 4150-4152 - Russian Issues
- DB 4200-4332 - Spanish Issues
- DB 4400-4699 - German Issues
- DB 4700-4704 - Belgian Issues
- DB 4800-5199 - French Issues
- DB 5200-5299 - Scandinavian Issues
- DB 5300-5321 - Czechoslovakian Issues
- DB 5350-5449 - Italian Issues
- DB 05350-05359 - Italian Wartime Issues
- DB 5500-5699 - German Issues
- DB 5700-5999 - 'International' Issues
- DB 6000-6099 - Swiss Issues
- DB 6100-6999 - 'International' Issues
- DB 7601-7720 - German Wartime Issues
- DB 7000-9796 - 'International' Auto Couplings
- DB 10000-10147 - Swiss Issues
- DB 10000 - Swedish Auto Couplings
- DB 10500-10524 - Danish Issues
- DB 11000-11256 - Swedish Issues
- DB 11100-11256 - French Issues
- DB 11300-11357 - Italian Issues
- DB 11500-11596 - German Issues
- DB 11900-11909 - Nordic Issues
- DB 20001-20030 - Swiss Auto Couplings
- DB 20100-20177 - Danish Issues
- DB 20200-20227 - French Auto Couplings
- DB 20400-20406 - Austrian Issues
- DB 21000-21627 - 'International' Issues
- DB 21000-21546 - Auto Couplings
- DB 30000-30007 - Icelandic Issues
The first 900 recordings in the series (DB 100-DB 1000) are worth a brief exploration at this point as these early recordings set the foundations for the rest of this fascinating series.
Many of these first issues were nothing more than reissues of acoustic single-sided celebrity 78s which were often coupled to suit the newly introduced two-sided format.
Some however, were recorded both acoustically and electrically specifically for inclusion in the series. Some recordings were also taken from HMV's American affiliate, Victor - including the Cortot Chopin 78, (DB 853) which was recorded electrically, and the first electric recording to be issued in the series.
Interestingly, the first 290 recordings or so featured only 'celebrity' singers. The first orchestral recording did not feature in the series until issue DB 369.
1 Semeonoff, Boris; Record Collecting; Oakwood Press; pp.15 [2nd Edition]
2 Discography of American Historical Recordings, s.v. "DB-853 (12-in.), accessed January 3, 2016, http://adp.library.ucsb.edu/index.php/object/detail/79316/Gramophone_DB-853
3 Kelly, Alan; Volume 4 - The International Red Label Catalog; Oakwood Press; pp.2