Thanks Bob,
i had yesterday entered time machine and left it 20 mins and not seen anything prior to the day before.
This morning i tried again, this time time machine was preparing a back up but i entered any way, came back 15 mins later and it was populated with entries back to June 2019.
i have heard/used a technique for mounting time capsule drive first and then opening time machine and you can then see the historical backups but its not ideal.
i didn't know it was a common issue, Apples Time Machine page had no mention of it and a forum search before posting provided me a bunch of old links & i didn't bother filtering for most recent assuming apple would tell me the most pertinent entries.
Checking again now first attempt saw the historical entries within 40 seconds, 2nd attempt was ~ 20 and all subsequent attempts is ~ 15 seconds.
Something is working much better.
will be taking a read and looking at T2M2 and some other tools over at https://eclecticlight.co/consolation-t2m2-and-log-utilities/ some good reading there too.
As is often the case a problem shared is often a problem resolved i suspect it was the Time Capsule reload (i've read to leave it off at least 10 seconds so it will do a disk check) that did it and a couple of successful auto backups over night.
as a recap
i had mounted time capsule and had disk utility check the disk and sparse bundles
powered off time capsule for 20 seconds
once time capsule was up i checked time machine and didn't see an improvement
on my 10.12 machine i checked its time capsule backup and could see its full history.
left macbook pro running 10.15.4 over night which completed several backups
Checked macbook pro in the morning, leaving time machine open for at least 15 minutes and saw the history, all subsequent time machine checks showed the full history in less than a minute, eventually ~ 15 seconds.
I only rebooted the time capsule, no mac's where reloaded.
