Notice there are no second numbers that go beyond 4. They have 5-9 yet to go. With the third number they have not gone past 5 with the exception of the 501/508/510 series. The 501/508/510 series could be coming to an end or redone with the second number to change. What is next, only two digit numbers followed or preceded by a letter or two? The 10 series, the 20 series, etc. each unique in its own way. Or perhaps the 3HD42. Perhaps they should have changed the coding of the boxes again like they did when they went from legacy to DishPro going from four digits to three digits.