S7 Counter/encoder question

I need to program a machine what must do the following:

1 Motor with encoder. On this conveyor I have several machines. (Cutters/sprayers/fillers). The speed of the conveyor is fixed per product but can be different for other products. The position of the cutters/sprayers/fillers is known.

A spot depositor drops a filling on the conveyor. A cutter downstream cuts the product to a fixed length with the drop exactly in the middle. The lenght of the products is adjustable per product. So product A can be cut to 100mm and another product B can be cut to 80mm.

My question. I know how to use an encoder that is nulled once every cycle. (By proximity switch or so) But in this case there is no zero signal. The encoder just keeps on counting. How can I use this counter value to determine when to cut/spot deposit?

What happens if a counter overflow happens? Does this affect the cut/spot deposit?

Any tips on how to do this?

You must have some method of knowing when the product is either placed or cut and this must serve as your encoder zero signal.

Here's the code I use for dealing with encoder rollover (I use the ET200s counter module). Note that:

iLastCountA is a STAT integer
iCurrentCountA is the value read from the counter
iPulsesA is the pulse count this scan
diPosition is a STAT double integer
bZeroPosition is a boolean used to reset the position to zero