I just noticed this in some William Younger records for 1940.
It shows how ullage - returned beer - was being added at racking time. Sounds like a good way to fuck up your beer. 10 hogsheads (15 barrels) for a batch of 135 barrels. That's about 10 ullage.
Funnily enough, it's always the same beer: LAE. Not sure what it was. Perhaps it was a pasteurised bottled beer. Then the slops might not do too much harm. Pretty sure it was some sort of Pale Ale, judging by the hopping rate, which was relatively high. At least by Scottish standards.
They only seem to have mixed in ullage a few times. Either that, of they didn't record it in the brewing log.