More on Odometer Discrepancy + spark plug Question

["Mike Theuri" <mikesoft@conwaycorp.net>]

The former owner called me yesterday to let me know
that she forgot to mention that the odometer broke down
in September. She says she didn't use it for one month
and that she probably put about 3500 miles now that she
also had another vehicle. I won't have to worry much just
as long as it wasn't 15+k miles extra. The engine sounds
good and performs excellently.

My question revolves around the spark plugs. She said
she put one prong bosch spark plugs. Audi recommends
3 prong plugs. Would this have any effect if I changed them
to 3 prong ? Would a tune up be immediately necessary ?
Thanks.

Mike Theuri
'88 80 Q