The word "average" is a key word in my post. Yes, that would mean there would be 25 on the roster. But, there is always attrition with injuries, transfers, off the field problems...etc. It's unrealistic to think that every lineman is going to be here for 5 years.
So, if you have 5 per year over 5 years, that's 25. If you want to really have 17, that means 8 of the 25 don't make it 5 years. Heck, sometimes they don't even make it to campus. I think that's a reasonable expectation.
Also, if we have 5 this class, that means the last three classes would be 6,3,5. Or....an average of 4.66. I don't think it's unreasonable to think we would take 5 in this class.