From a post by burkitt on the District Dave forum, sounds like things are ramping up:
"I was on the visit to the CLIP project at Acton organised by
TechSoc last week. Testing of the first completed train is continuing. This is actually known as Train 3, with Train 1 having had only the replacement traction system, and Train 2 only the new passenger info systems, as trial runs. Train 3 is the first with everything fitted.
They were working on Train 6 during the visit, and aiming for an eventual 50 day turnaround time."
And a post from xmw:
"Further info for anyone interested
Train 1 & 2 were prototypes, so were stripped down and being built into the 'proper thing'
Train 3 is heading for the South Ealing test track (Currently stabled in Northfields depot)
Train 4 should be ready soon
No word on train 5 yet
Train 6 as you said, currently in the works"
So if they're aiming for a 50 day turnaround time for each train, and I presume there will be 2 that can be worked on at once, presumably we'll be seeing a new train every 25 days. That sounds fairly swift but on that trajectory it will take 7 years to get through all 85 trains. That's a long time.
So some of these 92 stock have got a long way to go yet until they get refurbished.