Hello everyone and first of all congratulations for this great forum.

I am new user and even though I read many, many threads in this forum, and others across the internet, I still don’t understand some terms regarding my smartphone.

I have model A510F and here are my current firmware:
AP:A510FXXU4BQC1
CP:A510FXXU4BQC1
CSC:A510FOXA4BQC1

1.I understand that CP is modem firmware, so, what is the difference between PDA(AP) and CSC firmware? Why do we need CSC since AP decides firmware updates? Are the country codes 2 digit or 3 digit? What information do I get from these 3 codes? (XXU vs OXA?)

2.Using the app Phone Info I found that product code is SM2A510FZDAXEO. I believe XEO is from Poland which is true, because even though I bought the phone here in Greece, the seller imported it from Poland. So, overall, now we have XXU / OXA / ZDA. How are these connected?

3.Is it generally a good idea to change the CSC to EUR, which is Greece, since I live here or shall I leave it as it is? Do I benefit from something?

4. Both EUR and XEO are unbranded codes. I see that in EUR latest android is version 7 but for XEO is 6. So….what makes it such difference? I mean, since they are not carrier dependent who is stalling/deciding the upgrade to v.7 in Poland?

I am really sorry if those questions sound noob to you but I would really appreciate it if someone had the time to reply and explain or post a link for me to further study.

Thank you in advance.