What happened to Formosat-4 and Formosat-6?

Question

Formosat-5 (see also Gunters) is expected to be deployed along with Sherpa later this year.

I noticed that before 5 comes 3, and after 5 comes 7. In that part of the world the number 4 is like a black cat with 13 painted on one side and 666 on the other walking under a ladder at midnight. Depending on location, you can find floors enumerated as 4 missing from hotels and room numbers containing 4 missing in hospitals - you just don't mess around with 4 if you can help it.

But 6? Gunter's space page shows little more than a placeholder, and other web sites (see screen shots below) have no mention.

Was it just cancelled, or was there trepidation also because of a quirk of language. I'm told that the number 6 can also sound like a word for "falls down" and so would be particularly unlucky for a satellite, but I am not sure if this is a coincidence, an amusing story, or turns out to be at least partly the reason.

For this answer, I need someone who actually knows the answer or can find a credible source, not just a quick copy/paste/forget. Thanks!

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above: from http://www.nspo.narl.org.tw/en/

above: from http://www.nspo.narl.org.tw/tw2015/projects/FORMOSAT-5/program-description.html using google translate in Chrome.

above: suggestions for a recent internet search

Answer 1

According to "The fast development of solar terrestrial sciences in Taiwan" by Liu, J., Chang, L.C., Chao, C. et al. there is no Formosat-4:

The pronunciation of “4” in Chinese sounds like “death” or “bad luck”, which is somewhat similar to “13” in West. Therefore, there is no FORMOSAT-4 mission.

and Formosat-6 was canceled:

FORMOSAT-6 was designed to have a remote sensing mission and, however, terminated after a careful evaluation.

Some of the authors of this paper are among the scientists involved in these projects, so I would consider it an official statement.

From what is available on Gunter's, it is possible that Formosat-6 was cancelled because of the suspension of development of the Taiwan Small Launch Vehicle (TSLV):

FORMOSAT-6 was targeted to be launched by TSLV (Taiwan Small Launch Vehicle) as the first choice. Due to the fact that there will be no propellant system to perform orbit adjustment, and therefore the satellite will be injected to its final orbit directly. The satellite will also be designed to be compatible with other international piggyback launch opportunities, as the development of TSLV has been suspended.