Below is a table showing, to the best of my knowledge, the different versions of the Pro Staff Midsize rackets and their distinguishing characteristics (also see legend below the table):

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chronol. order NAME BC CODE CODE LOCATION MIDSIZE BUMPER TENSION PRIMER FINISH ORIGIN 1 PS WHITE xxI BOTTOM X2 NO 65-70 RED MATTE CHICAGO 2 PS WHITE xxQ BOTTOM X2 NO 65-70 RED MATTE SV 1a xxB BELGIUM 3 PS WHITE xxQ BOTTOM X2 NO 55-65 RED MATTE SV 4 PS WHITE xxQ BOTTOM X2 YES 55-65 RED MATTE SV 5 PS WHITE xxQ BOTTOM X2 YES 50-60 RED MATTE SV 6* PS WHITE xxQ BOTTOM X1 YES 50-60 RED MATTE SV 7 PS WHITE TOP X1 YES 50-60 GRAY GLOSSY TAIWAN 8 PS WHITE TOP 85 YES 50-60 GRAY GLOSSY CHINA 9 6.0 WHITE TOP 85 YES 50-60 GRAY MATTE CHINA 10 6.0 BLACK TOP 85 YES 50-60 GRAY MATTE CHINA * there should be line 6a identical to line 6 except butt-cap code Qxx chronol. order: order in which model was manufactured with respect to time name: PRO STAFF or PRO STAFF 6.0 code location: at bottom or on top of "W" on buttcap MIDSIZE: written on outer edges of throat: x2 = writte on both sides; x1 = appears only on one side; 85 = MIDSIZE 85 origin: SV = Saint Vincent Island, West Indies NOTE - in the blank row there sould be mention that some pro staffs were briefly produce in Belgium by Donnay with buttcap code xxB.