You should only write what it asks for.
Funny ha-ha !

I have just written a letter to SWT. I use the Royal Mail's "print your own" postage system. It has recently been "upgraded" (which I think means ******-up in the guise of improving it).
When you try and address the envelope certain items are mandatory, like a person's name. It won't let you put in Mr Customer Relations Manager, 'cos that's too long, but I don't know if it is Mr Smith or even Mrs Smith !
Next requirement is a house/flat number - SWT (like many organisations !) occupy a building, not No 3 Acacia Avenue.
Why don't they just give you 6 blank lines to put in what you want ?
PS: Guess what isn't mandatory: The Postcode !!!