I have been working on 72/73 CT 175 for years now I am into 72/73 DT 250.My 72 DT has a 19” front wheel but when I went to purchase a front wheel for the 73 DT my Yamaha shop Manuel says that Yamaha switched to a 21” in 73, is this true. Partzilla and other sites show the 73 DT 250 is a 19”.Witch is correct.Thanks for your help.

72 front was a 19" , and 73 was a 21 " . Most online parts lists combine 72 & 73 , and don't differentiate
where parts have changed , which parts go with which bike .
There weren't many changes between the two  , the front wheel being the most notable .

If I remember correctly, the steering lock was new for 1973 as well?