The OWE fare rules state
Baggage regulations
Two free pieces of 23 kilos each shall be permitted. Additional allowances may apply. Refer to individual carrier websites.
As an F passenger, you will generally receive more than this allowance from individual airlines.
This would still apply on any segments that don't have an F cabin, as you would then travel in J and the J baggage allowance is typically more than the OWE rule allows.
I have no idea why your tickets have sometimes shown 3 pieces for the entire trip.