>>These envelopes certainly could be used for tipping if you choose ut they have not been put there for that purpose.<<
Yes, that's correct. However, I have always just used them for that purpose.
>>I have always used the personalized writing paper for thank you notes I have written to various crew while abord.<<
Yes, exactly. And that's what I've done. I don't just tip them, I also write them a thank you note using the complementary stationary.
Grace and Peace,