LOCA glue in one area or two?

You are correct. Typically there three layers of a smartphone screen, which are all glued together.

Normally when you replace a screen, you replace all three at once as a complete unit. Some people like to save a couple of bucks by reusing the LCD screen and gluing a replacement touchscreen unit to the excisting LCD scree. Please be adviced, this is a complicated procedure and takes some experience to complete successfully.

While it is possible to buy the glass separately, I don't recall ever seeing a touchscreen unit for sale separately, at least not without the front glass already glued to it.

This goes for smartphones. Tablets are a different story. Typically the LDC screen is separate to the touchscreen, i.e. not bonded to the screen directly. If you want to replace the glass, you replace the glass and touchscreen interface together as one unit - there is no need for LOCA glue here. The glass/touchscreen fron of the tablet is mounted to the front of the tablet using doublesided tape.

Please refere to the following guide: https://www.youtube.com/watch?v=UNXYPS4y...