NEC TSC: Frequency of Price Adjustments for Inflation when using NEC4 TSC + X19

I'm trying to understand what the typical frequency is for calculating price adjustments for inflation. Is it normally done monthly at each assessment interval or on a less frequent basis? Also would the frequency possibly be different based on which Main Option is being used?

If it helps I'm asking the question in the context of a Highway Term Maintenance Contract which could be using more than one Main Option for example Option A for Planned Highways Maintenance and Option E for Reactive Maintenance.

Thanks in advance.