First there are three important dates that change the level of information released to someone who is not a close NoK (defined by MoD as subject or their spouse.
1. Up to 25 years after death Only really acknowledgement of service and overall time from enlistment to Non-effective status. - usually more redactions than remaining print
2. More than 25 years after death, open to everyone on request - this is proven by inclusion of either a copy of a death certificate/presumption of death or CWGC link if they died in service. If proof of death not included with application redaction inline with 1 above applied. If valid application then service record with redactions to identifiable personal data, military penalties and medical events.
3. 115 years after birth, open to everyone on request - no need to provide proof of death. Full record mostly available but in some cases still redaction to living persons, medical and military penalty.
So what you received depended on information provided - but at only 20 years since death you should have only got bare details of service.
Service records rarely have details of PoW as the person was still classed as posted to the original unit but is listed as Non Effective to allow the unit to replace them.
Ross