EMS tracking on return envelope?

[new2here]

I’ve noticed that the last 2 times I have done my 90-day via post (to CW) I enclose all the paperwork required, a self-addressed envelope with B40 postage (it’s more than needed, but that’s fine) AND an EMS tracking number.

 

The EMS tracking label isn’t the EDI-generated label; I’ve been told that they (EDI labels) can only be printed and used when the exact postage is paid AND it is mailed at that time.  It can’t be used for future-use... ok, that seems fine as I know the tracking data also uploads based on the EDI label being generated.

 

so... the last two times I have had my return EMS label; the “older” version that’s orange, white and blue, that I put on the return envelope replaced/covered by a new EDI-based label when Immigration tenders the letter at CW Post office.

 

Yes, I still got the letters back.. it’s never gone missing..  but it is nice to know when the letter actually is sent.. plus, if they (immigration or Thai Post) are overlaying a new EMS tracking, how would I know this, thus, IF it were to go missing, how would I know this much less go about tracking it?

 

i did ask my local post office today (I live not far and had business there anyway) and they said that they are not aware of any official postal policy that prohibits the use of an EMS label being applied to a letter BEFORE it’s actually given to the post - only that you can’t use an EMS label if you didn’t affix the correct amount of postage (obviously) 

 

Anyone have insight?