The only instances I've had something like this happening is with very old (40+ years) decals. Those are usually identified by the yellowing of the decal's transparent portions while still on the paper. But those become brittle more than that they tear (they simply disintegrate in the water

).
Also; there are several thicknesses of decals available, and some tear more easily than others.
What you can do in such a situation is to spray the decal sheet with clear varnish. Two thin coats will do. Then you can use the sheet as usual, but make sure that you cut out the decal as close to the printed part as possible, since the varnish will cover the entire sheet and it might otherwise tear because of that.
The rest is business as usual then
