It's a good question. The fact that in the first show on January 1st, and again for Cheltenham and The Grand national there is a fair amount of the BBC Sport and Channel 4 footage, makes me wonder if Horse Racing now operates similar to how FOM run the broadcast archive for F1.
All live race rights holders have to give the 'tapes' of each race, to FOM which is then held in their archive.
Rights holders both past and present. As long as you have the rights, you have access to past races in the local language.
That's how with Channel 4 and Sky Sports you have a lot of Murray Walker commentary - and no caption over the footage 'pictures from BBC Sport'.
Wonder if when Channel 4 won at the last but one rights renewal, they got access to the BBC Sport coverage (via the HRA) and now ITV have both the BBC Horse Racing archive (of what exists) and the Channel 4 coverage.
My user name might look like Hatton Cross, but it's pronounced Throatwobbler Mangrove.