The agents you talk to in the call centre are repeating what company policy is - names have to match. However they are not operationally aware of what happens at check in.

Check-in agents deal with mangled names every day, every shift. They are used to names being typo'd, being in the wrong order, truncated, transliterated differently, and just generally being misrepresented by the antiquated technology that backend airline booking systems use, and the elastic bands that try to work as integrations between them. A truncated name is not going to be anything to worry about, provided that what there is of the name is a decent match to the name in the passport being presented, you have nothing to worry about. At the check in desk don't draw attention to the issue yourself, and if it happens to be mentioned by the check in agent feign surprise "oh is it, how did that happen?"

The name on a ticket does not have to be a direct match to the name in the passport, it just needs to be a good enough match that the person checking in correlates to who the ticket is meant for. Low cost carriers with more modern systems like to enforce a match because their systems are standalone, don't have the legacy issues that cause the manglement, and they can use mismatches to extract more money. But legacy carriers with legacy backend systems and data being shared by other systems and services have to accept that names won't always be 100% right and the passenger is often innocent in such matters.

The API (passport) data does have to be accurate BUT this can be sorted at check in and corrected, and is usually fixed/confirmed by the check in agent using their kit to scan the machine readable zone on the passport.