Hi David,
Before the highly praised website upgrade (!) there was a way to get all your old history as you mentioned - see end of this post - but as you say that doesn't work any longer.
I know some folks had problems initially on the new website even going back more than 3 months meaning they had to choose the custom date range but then be sparing in the date range (keeping the gap between start and end date under 6 months) but that still only got you back 1 or was it 2 years?
It seems to work properly now though on date ranges but only allow a rolling maximum of 3 years so nothing earlier than 17/07/2017 as of today, then by tomorrow that will become 18/07/2017 etcetera. I even tried manually typing in earlier dates but that just gives an error

Sorry I don't have the answer for you but perhaps someone has found a clever workaround on the new website like there was for the old website or it may be something Flying Club themselves can extract and email for you at least a year or two further back than the seemingly rigid rolling 3 years as I'm sure I saw someone post on here in last year or so they had got that from FC to help resolve a TP query they had.
Best of luck,
Tim
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The tip from International Hitman that I had seen, but not acted on, before to see your history from year dot:
"There is actually a way to see all your history --- Log into your FC account, on Your Account Summary page scroll down to "Last 5 transactions" and press the Update button beside it --- URL line changes and middle section will say statementSelection=0 change the 0 to an 8 and Hey Presto -- your statement from the beginning of time"