Hello Grimtine!
I suppose we are talking about the Megapack, I did not upload any more new asset packs in the bundle recently, but I did upload some updates for some existing packs. For example the misc items ( update 2 ) have some new props, the Chainsaw has a (Chainsaw 2.0 version, when downloading) etc.
As for the second question, if you bought the asset packs, credit is not necessary, you are free to modify the assets/textures as you like but my only requirement is to not 're-sell' the assets.
The new knife&chainsaw should be available when downloading the old versions too.
If you still can't find them or have any missing asset packs, send me a friend request on discord ( wielen ) and we'll solve it :)
Thank you for the message.