To DST or not to DST.

Currently the TZ DB has Tonga moving to DST on the 5th November.

In 2016 they announced they were resuming DST, in the only reference to that I could quickly find, does not state that this was for one year or whether the resumption was also for successive years.   No reference for the change was added to the TZ DB.

IATA it seems have taken it as being for a single year and so do not have DST starting this year.

Given the discrepancy between IANA and IATA (besides the letter T), does any body have any authoritative/corroborating source for either position.

/David