Summary on Percentages of Original Japanese BGM/OST kept in the Pokemon Anime International Dubs Only (Does not include the Movies or Pikachu Shorts, That List is Below It But Also Present In the Document...presented with commentary to demarcate the changes in companies & such for your entertainment):

- 4Kids/TAJ Era -

S1: 73.3%
S2: 69%
S3: 72%
S4: 37%

AVG = 62.9% (More than half is kept, though once mid Johto hits, they slash the amount kept- I think the Johto fillers broke 4Kids & TAJ on this aspect permanently here...kidding, they likely decided to put more in house stuff for royalties by this time as 4Kids would take the exact reverse path with the Anime-- with the Movies & Pikachu Shorts simultaneously here-- see the Document above for this)

- Later 4Kids Era -

S5 (Taken in house late into the Saga, TAJ removed by Address Unown): 33%
S6: 30%
S7: 27%
S8: 20%

AVG = 27.5% (A little more than one in every four pieces is heard originally in the Original Japanese Version, and still retained, a lot better than conventional wisdom would have you believe about this Era but at the same time, S8 is kind of scary and worrisome but TPCi replicates this by S16 to be fair!)

-- Entire 4Kids Era Average: 45.1% (Close to almost half kept on average as the first 3 Seasons keeping so much and never heading south of 20% at their worst musically, led to this number) --

- Later TAJ/PUSA Era -

S9 (TAJ snags back the rights from 4Kids after TPCi cuts costs on the production & replaced the original 4Kids dub voice cast, writers, singers with the current TPCi dub staff etc known for the Pokemon USA recasting controversy): 26%
S10: 34.3%

AVG = 30.2% (Almost the same as the later 4Kids Era, three in every ten is heard originally in the Original Japanese Version, negligible difference really)

- Early TPCi/DuArt Era -

S11 (TAJ goes out of business, DuArt is given the reigns): 44.9%
S12: 47.0%
S13: 38.3%
S14: 92%
S15: 36%
S16: 20% (Isn't it funny how DuArt ended up taking the same path as 4Kids & TAJ under TPCi did by Loeffler's end here? Exact same bottomed out moment by Season 16/late BW at 20% w/Loeffler's final Season)

AVG = 46.3% (Less than the 4Kids/TAJ Era, more than the late 4Kids & late TAJ Era, but goes to the very worst of 4Kids by the last season at 20% and worrisome- Loeffler repeats History here!)

- Later TPCi/DuArt Goldfarb Era -

S17 (DuArt gets rid of John Loeffler, Ed Goldfarb takes the reigns for TPCi): 19%
S18: 17%
S19: 15%

AVG = 17% (Less than the entire 4Kids run & even the later TAJ run as well, yikes!!! Only a little over one and a half cues are the same as in Original Japanese, very scary!)

- Modern TPCi/Goldfarb Iyuno Group Era -

S20 (DuArt goes out of Anime dubbing in business much like 4Kids did by 2011 & TAJ did by 2008, SDI Media/Iyuno Group given the reigns by TPCi and it is bicoastal recorded nowadays): 15.1%

Lists Incomplete from Here On, But By Word of Mouth & Still Need to be Completed

S21: 9.6% (Incomplete; Halfway Through Done On Document)
S22: 12.3%
S23: <8%
S24: <8%
S25: ???%

S22 List (Update 5-19-23!):

View attachment 170496​

Current Avg = 18.3%

-- Entire TPCi Era Average Run: 31.8% (Through mid Season 21, not including the rest of it through Season 25 which would bring this average lower!) --

MORE TRIVIA

Early 4Kids/TAJ kept the most of the OST on average from especially mid Kanto to the end of early Johto (they only kept as many cues roughly in EP001-EP011 as in the last Season of AG under 4Kids, Dogasu's reviews have errors there & it took until EP012 before things slowly got better: the avg. for Kanto is so high because of the rest...not EP001-EP010 which is on par with AG093-AG145).

On the other hand, TPCi w/SDI Media/Iyuno nowadays kept the least of the OST on average from XY all the way through JN (progressive decline for TPCi in the later DuArt years in how much was retained, much like later 4Kids, later TAJ, and later PUSA but none of the three ever to their credit got to the lows TPCi did with later DuArt and especially nowadays w/SDI Media).

I find it hilarious 4Kids' dub kept more of the OST as a whole if we consider all 25 dub Seasons than TPCi's dub did in their own (you would think TPCi would have kept more from the games this Series is based on, but they ordered Goldfarb & Gopal to replace more of it than Loeffler & Corallo ever did even under their own wing).