Unfortunately data is not available, before 1999, except in the case of various individual champions and opp sex champions (and even then their published totals are unreliable). Where a champion won with say 120 points, there could have been a close runner-up (same sex) with 118 and there would be no record of that at all.
A claim could in theory be substantiated with a very large stack of brevet cards or a very long list of brevet numbers, but I doubt if anyone would be willing to undertake totting them up, other than the claimant him/herself.
As well as Liz Creese, I know of at least one other person who would claim to be on the list - but unverified, and I can think of one or two other people who have been higher-than-average achievers over an awful long time (25+ years), who've probably never even thought about it.
In Liz's case her 1000+ total can be easily seen from her Championship-winning years alone, in the Handbook as 102, 151, 159, 122, 157, 222, 100. No-one else can be verified that easily, unless they've done it entirely since 1999.