Firstly, you need to be aware that there are mistakes and omissions in those cards so you need to look at them carefully. They are not a complete record of service. CR1 cards were completed in a port MMO at the same time a Dis.A book was issued or an old one checked.
Not all contain the same information as there were changes made to the cards through the years.
CR2 cards show individual seamen's foreign voyage start details. On the back of the CR2 should be a list of his ships usually by official number but sometimes a name with dates of foreign voyage engagements.
To be honest, I would need to see the cards to give you a proper answer to your question though.
If you could give his name and date of birth I can look him up and check for you. Give it in a private message if you don't wish his name to be public.
Of course there is another way to find out when he joined and left the ship in 1924/25 and that is to look at her Crew Agreements. There is one for 1924 but none for 1925. If she was away from the UK in 1925 and did not get back until 1926 then it is likely that the 1925 Crew Agreement is filed along with the 1926 document. This is held at the Maritime History Archive in Canada.
Your other question - seamen signed on for the duration of the voyage whether it was two weeks, two months or much longer. On completion of the voyage they could sign off or sign on again for another voyage assuming the master was happy with their ability and conduct. They could also leave and go sign on another ship. Seamen on some occasions never completed a full voyage. Sometimes they would sign off at another port or actually jump ship.
Hugh
