as the title really, how long ago would you have had to build a kit to avoid SVA but still have it legally registered (ie correct description on V5)? Cheers!

The test started in 1998

There was a period of grace up to Jan (?) 2000.

If I remember correctly, I had my first car inspected by the DVLA at home in 1998 - sort of part built - and given the chassis number - then I was allowed to have just an MOT to get on the road some time in 1999 even though the SVA was already started.