This is a very confusing conundrum. On All the GMPTE maps, Knutsford, Ashley and Mobberley are outside the GMPTE area. Under the GMPTE instructions, fares to "Manchester CTLZ" are only available from stations within the GMPTE area, while fares to "Metrolink City" are available from stations outside the GMPTE area. Fares to just Manchester should be to "Manchester Stns" from outside the GMPTE area.
Now, therefore, Knutsford, Ashley and Mobberley should have fares to Manchester Stns or Metrolink City, while Hale should have Manchester CTLZ or fares to the Metrolink zones (A to H excluding D). BUT, all 4 stations both in and out of the GMPTE area have fares to Manchester CTLZ Rte Any Permitted, AND Metrolink City Rte Altrincham. So it all seems a bit odd.
In the Fares Manual, in the GMPTE section look under the heading "Journeys to Metrolink from Within the Greater Manchester area". This would not be a logical place to look as 3 of the stations under discussion are outside the GMPTE area so you would look under the different heading. But, it does list a destination of "Metrolink City - Only used from Knutsford, Ashley, Mobberley and Hale for journeys via Sale", which obviously implies you must go on Metrolink from Altrincham. However, this information appears to be printed differently on the ticket itself.
Thus, it would seem that up to Knutsford is both inside and outside the GMPTE area depending on what ticket you have. Talk about confusing!