1. Validity of PSK2k-QSOs
The goal of the IARU-QSO-Rules is that in a radio contact both stations confidently receive the other callsign, a report, and a confirmation that the other station received the corresponding information.
The PSK2k-mode was designed with the goal to optimize both, the sensitivity in a meteor scatter communication on 144 MHz, and the confidence of a QSO in the sense of the QSO-rules.
The confidence into any PSK2k-QSO can easily be deduced from the capability of the error-detection of the checksum algorithm. A QSO needs 4 successful transmissions. The probability of a successful QSO with a wrong callsign is 1/(16381*32749*32749*32749) = 0.00000000000000000174.
This probability is so small, that if a million amateurs each makes a thousand contacts every day, then only one single faulty QSO could be logged on average in more than a million years.
If these million amateurs intentionally call the other station a thousand times per day with one wrong letter in the callsign, then in the average one QSO will be logged in 50 years, all other 17568573373380 trials will not reach the final confirmation.
The above calculations only are based on the reliability of the checksum algorithm. There are additional powerful tools in PSK2k which further reduce the probability of errors.
2. Compatibility with the IARU Recommendations for Meteor Scatter QSOs
The goal of these recommendations is to minimize problems in meteor scatter QSOs using SSB, HSCW, or FSK441. The operation of PSK2k is very similar to that of FSK441. But it differs considerably in the encoding and especially in the concept of gaining reliability. The consequences for operation are:
(1) If any information appears on the screen (callsigns, reports, etc.) you can trust it. You never need to receive something twice.
(2) The encoding of PSK2k is not character-oriented. Therefore the usual form of reports in HSCW or FSK441 is not adequate. PSK2k directly displays the SNR of a received signal, and it sends this as the report. The length of bursts is not measured, because PSK2k - other than HSCW - is a meteor scatter mode, which mainly uses the very short and weak reflections of underdense meteor trails.
(3) There is no need to use different frequencies. As long as there is no local QRM by each other caused by the well-known tx1st/tx2nd-problem, all PSK2k-QSOs can run on the same QRG. The recommendation for QSY frequencies therefore does not apply to PSK2k.
(4) A CQ in PSK2k not only sends the callsign of the caller, but also his actual QTF. Therefore operators are encouraged to monitor the calling frequency and to reply to received calls if the QTF fits. Skeds can be made. But it is recommended to start even a sked with a CQ-call.