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Variable contrast filters do fade, so I wouldn't recommend old filters when you are learning printing.
And as Kodak Polycontrast paper hasn't been manufactured for several years, I wouldn't recommend learning on Polycontrast paper.
The Kodak filters - even the newest ones - also haven't been made for several years.
The Ilford Multigrade filters are being currently manufactured, and they are perfectly matched to the Ilford paper that is also currently being manufactured.
There are other, house brand papers that are a bit cheaper than Ilford. Most likely they have been checked to confirm that they work with the Ilford filters.
The most recent Kodak filters are badged as Polymax filters. In some special circumstances, I use them with the Ilford and Oriental papers I use, but I have enough experience to be able to tell if they are working in the way I require.