Speaking only of Army ROTC:
No, it is not limited in amount, but is limited in time frame. Yours is a 4-Yr. Others, perhaps most to Privates, are called 3 Yr. Advanced Designee. Yours is for Unlimited Tuition and Fees, for four academic years (8 semesters, 12 quarters). Summer school is not paid for unless it takes the place of one of the quarters/semesters. An eleventh semester/13th Quarter is not paid for except by petition, and only applies, from what I have read here, for specific circumstances around some Engineering Majors at some schools.
If your tuition+fees is $45,000 next year, that is what the Army pays.
As tuition and fees go up each year, no problem. The 2nd year, $47,000. The third year, $49,000, etc.
However, if you choose to accept the scholarship to pay for Room and Board instead of Tuition and Fees (which some might do if the Tuition+fees at some Public schools is less than room+board), there is one limit and one tax consequence:
1) limit is $10,000 per year
2) that amount is treated as income on your tax return.
The Book stipend is currently $1,200 per year. The Subsistence pay is currently paid at ten months per year, at annual totals of $3,000 for MSI, $3,500 for MSII, $4,500 for MSIII, and $5,000 for MSIV.
A scholarship Awardee doesn't get any book, monthly Subsistence Pay or Tuition+fees money until their Scholarship Award is Validated by the PMS on campus, and you sign your Contract. Validation means you enroll in the ROTC class, enroll in the ROTC Lab, and pass the APFT. Until then, no $$. The school will wait for their tuition+fees by arrangement with ROTC, but if you don't pass the APFT by the end of the first semester, the tuition+fees money is forfeited for that Semester and you personally owe the University.
Here is a copy of a blank Scholarship Cadet Contract. I haven't seen a filled-out one.
http://www.missouristate.edu/assets/milcsi/DA597_3_Scholarship_Cadet_Contract.pdf