…. That’s a very good point . Not sure why a visit to immigration to renew / extend etc a visa can’t be used to start the 90 days again . I’m sure there’s a good reason .
As Tod says , they will just look back at the required 2 months and they circle the date on your copy. Bangkok Bank are usually very good at giving your the letter on the spot (. Maybe 20 minute wait ) . I got mine at the weekend and then took that in on the Monday .