i don't know what you guys are thinking.
The suffix on Microchip micros has always described the type of package, nothing more.
Both of these devices come in an ML package. This basically means QFN. The 44 pin ML package is 8x8mm. The 28 pin ML package is 6x6mm.
/ML = QFN (6x6mm up to 28 pin, 8x8mm for the 44 pin)
/MV = uQFN (4x4mm up to 28 pin, 5x5mm for the 44 pin)
/SO = SOIC
/SS = SSOP
/IL = DIP
/PT = QFP (they seem to have stopped making new micros in QFP around 10 years ago, at least in the 8 bit families)
Some of these packages are not available in all pin counts. But all of the first 5 are typically available for both 28 and 40 pin micros.
Sometime you might see a "-T" after the suffix. This means the part comes on tape/reel. There are other suffix modifiers, but the package part "/XX" has been consistent for as long as I would know.