Technical Understanding the ECU code/notation/part number

[dblokillo]

I have issues with my ECU (I destroyed it) so I need to replace it. I was wondering, taking in consideration that I have read and seen lots of different variants of what seems to be the same ECU, I am very confused by what the codes and part numbers are in relation to what can be used. So, here is an example:

My ECU is the following:

The form factor, being a slim version of others ECUs I have seen before, is very similar to other's I've seen on eBay, say this for example:

However the code (the IAW code I mean) is completely different, mine being IAW59F.M3 and this other being IAW5AF.P4. I am quite sure that I could buy this, plug it into my car without issues, and it would not work because it's a different code.... or would it?
So here is my question, what makes the difference between those codes and others? What does the part of these codes mean? If the ECU is virgin does it even matter? Also, the HW version also plays a roll, as I understand, and I could swap a HW003 for a HW303 as per a different post. Would that work for any HW number?

Lastly, my ECU has a part number 46808846, but in my trusted parts store (I buy from there all the time and they have a very reliable catalogue) I see 3 part numbers that do not coincide with mine at all, one: 46820323, 46825210 and 46825208, and looking for them I see that one has a code IAW59F.E4, different from the M3 that mine has. The others seem to share at least the same code...

I am SO confused with this!

 

[ceecff]

Hello,
check with your VIN in ePer, each ecu is programmed different (engine, sensors...) so you can't use anything.
New ecu must be virgin (self coding) so you can use it like original.

 

[Mike1alike]

You cannot use other code than what's on yours.
Virgin ECU refers to IMMO. It needs to be virgin so you can use it plug and play. If it is, the first time after you connect it and you turn the key on it will memorize the IMMO code from your key and it uses it on every engine start check. If it's not virgin, the code on your key doesn't match with the code stored on ECU and the engine won't fire up, you'll get IMMO error.