Because you are working Offshore, so have good reason to come and go frequently. "Good reason" meaning, other than to abuse Visa Exempt Rules, for purpose of being perpetual Tourist without a Visa. And, of course, you are right, No Overstays doesn't hurt your case.
That explains it. YOU have a valid reason for your repeated entries, which obviously satisfies the Immig. Officers. Not so, for folks, just trying to use it to indefinitely stay in Thailand, without getting proper Visa(s).
When you pass thru Immig. Control on arrival, and the Immig. Officer Stamps your Passport with Permitted Stay Until " .....", he enters it into his computer.
Not sure what you mean by "Retirement Visa". You seem to imply you are already in Thailand. If that is the case, there is no Health Check requirement, for 1yr Retirement Extension of Non-O. Likewise, if you were on an O-A Visa, then the requirement is for mandatory Health Insurance.
is correct. Use TM7, 1900 Baht, and the financial requirement: 800,000 Baht in Thai Bank (seeded for at least 2 months prior to applying for Extension).
90 Day Report applies to "Long Term Stay" only; and if you received an Extension of Stay, the date for your initial 90-Day Report should have been provided to you; and then calculate additional report dates yourself.