1936 Manila-Batavia First Flight Cover

This is my first post, wherein I'll be having pictures in each post as to provide visual information on what I wanted to share. Technically, I'm not an expert that can provide accurate facts about my collection. That's why I'm only telling what I know based on what I've read and learned from other collectors. Perhaps someone could also help me if they would share information and other interesting facts on what I'm showcasing, so that I may learn as well.

This is the scan of my first cover of first flight from Manila to Batavia:

I would like to thank my uncle for having my collection scanned in his place cause I don't have a scanner yet. I've got this cover from a good friend of mine, Mr. Coolpit. Most of my recent collection came from him. He is such a good collector, not only that he sells interesting items but also he provides interesting things about it.

Here are the closer details of the envelope:

Here is the front of the envelope which I forgot to scan, so I just took some picture of it instead:

According to Mr. Coolpit, the value of envelopes depend on different factors, such as the date, stamp (2 stamps above) that were used; different counter stamping; condition of the envelope, etc. So as to possibly say that the more the stamps there is or even in other case, the scarcer the stamped that was used could mean a higher value for the said envelope.

In addition to that, even the manner stamping that was used could also be factor(stamping of first flight, Batavia-Centrum, etc.) in having its value different from other envelope covers.

An additional info would be very helpful, as to know other facts about this issue. I hope you all like my first post and there's more to come.