Example of counting in 2024 CMS 117:

Has Appropriate Number of Hib Immunizations

• exists ( "All Hib Vaccinations" HibImmunization //union of 3 and 4 dose immunizations
  //4 dose test
  let HasFourDose: Count("Hib 4 Dose Immunizations or Procedures")> 0
  where ( HasFourDose //if pt had at least one 4 dose code
  and Count(distinct("All Hib Vaccinations" HibVaccinations
  return Global."NormalizeInterval"(HibVaccinations.relevantDatetime, HibVaccinations.relevantPeriod)
  )
  )>= 4 //pt must have 4 regimens (e.g., 3,3,4,4 or 4,3,4,4)
  )
  or ( HasFourDose is false //if pt did not have at least one 4 dose code
  and Count(distinct("All Hib Vaccinations" HibVaccinations
  return Global."NormalizeInterval"(HibVaccinations.relevantDatetime, HibVaccinations.relevantPeriod)
  )
  )>= 3 //pt must have 3 regimens of 3 dose codes
  )
  )

Compare this with the numerator description:

At least three HiB vaccinations, with different dates of service. Do not count a vaccination administered prior to 42 days after birth.

If you have 2 Hib vaccinations on the same day, but at different times, they would both count. You need to enforce day precision here. Another example would be 2 vaccinations with no relevantDatetime, with the same relevantPeriod low time, but a different relevantPeriod high time.

You should also consider counting datetimes instead of intervals in the unlikely case where relevantPeriod spans more than one day – maybe by taking the start of relevantPeriod.