Started using them around 1990. Funhouse was a title that had both screened and decal versions of its side art. The warning at the back of the head box was always silk screened on. Unaware of any MM being silk screened on? TZ was always a decal.

For IJ, I'm going to quote Bryan Kelly:

Bryan_Kelly said:

Now we're going to talk about whether IJ and games like it, were decaled or not. NO THEY WERE NOT!! But if you've ever removed IJ artwork, you'd swear it was a decal you were removing. NO IT WAS NOT!!
With earlier games, the artwork was screened directly unto the wood. At some point, Williams started buying their plywood with a vinyl outer layer applied at the factory. This gave them a perfectly smooth surface to apply the screening. This is not truly a decal, although it may appear so.
Looking at the top of the IJ head in pic one, you'll see what I mean. The same plywood was used for the top and here, I'm removing the vinyl layer. Remember, THIS IS NOT A DECAL!!

Source: https://pinside.com/pinball/forum/topic/ij-restoration-started (p1)

TZ was never a decal.

The vinyl will bunch up just like decals but it's not a decal.

Here is an excellent article:

http://www.flippers.be/pinball_cabinets.html

My T2 (1991) has what appears to be a decal as it is de-laminating from the leg area but it could very well be the vinyl coated plywood that you mention. However, the backbox looks like the sides were screened directly onto standard plywood as scrapes and abrasions show wood and there is some visible planking through the art.