Radar Observer is a national endorsement, it appears on a different page from your STCW endorsements. It needs to be up to date when the MMC is issued or it won’t appear in the MMC.
ARPA is not an endorsement, if you don’t have it, you will get a limitation on your OICNW and/or Master STCW endorsement “Not valid on vessels equipped with ARPA.” If you do have ARPA, there will be no limitation, and the term, “ARPA” will not appear anywhere in your MMC. ECDIS is the same. In contrast, GMDSS is an endorsement and goes in the STCW part of the MMC.
First Aid and CPR is not an endorsement and will not appear in an MMC. It is a requirement to get a national officer endorsement (license) and part of STCW basic training. STCW Basic Training is endorsed in the MMC.
Medical First Aid Provider is an STCW endorsement and appears in the STCW part of the MMC.
Medical Care PIC is also an STCW endorsement, and appears in the STCW page of the MMC. If you have medical care PIC, they will also include, or will keep, the Medical First Aid provider endorsement.
VSO and VPDSD are also the same, if you have VSO, VPDSD should also be included and in the MMC.