The rule of thumb: you shoul spend time in the US at least |
as much as you spent abroad last time.
You were out for 18 months. Re-entry permit is valid for 24
months. By the time you can leave US again it will be long
expired, this is why immigration officer did not return it to
If you plan to go out of the country again, be careful. Do not
do it before you spent 18 months here.
In case it is absolutely nessesary do not spend more than
179 days outside.
Greencard without Re-Entry Permit allows up to one year,
but there is a trap: if you spend outside 180 days and more
you have to prove that you did not abandon US residency.
If it is less than 180 days burden of proof is on immigration