Hmm so if I understand this correctly. I can use letters which are addressed to my old property as letters of correspondence. And for the accommodation evidence, I would require a letter from the new agent/landlord confirming that they are ok with me and my husband staying in the place?
Correct. The correspondence is to show that you and your partner have lived at the same address, which is why it's supposed to be spread out over the time period you're relying on. Since you two haven't been living together the whole time, you'll need to provide what correspondence you can and write a letter explaining that, and provide evidence of your regular contact when you were apart.
Regardless, you still also need to provide proof of accommodation for after your visa is granted... Home Office want to know that you will have a place to live if they let you stay. If you're renting, this proof would normally be a tenancy agreement and if both of your names are not on the agreement, a letter from the landlord saying it's okay for you to live there.
If you own your home, the proof would be the Land Registry document showing ownership, and the most recent mortgage statement if you have it.