Edwin Pawlowski wrote:

Many codes allow only two layers. I'd not try for three, but it has been
done. More likely to have problems down the road. If you have curling
shingles, definitely get rid of them.

I prefer the look of the "architectural" style over the three tab. No
disadvantage at all.

When roofer added new shingles over old several years ago, old shingles
were curled somewhat and he recommended textured type shingle to help
hide any imperfections. Looks great.

Reason for not doing more than 2 layers is excessive weight on roof.

Frank