It's a violation of the current rules. However, the rules also clearly state this:
"Note 1: Individual or team uniform, logo, number and shoe rules shall be enforced
through inspection by the clerk of the course or the head field event official at initial
event check-in. Violators shall be warned, given the chance to correct the violation,
and reported as provided in the rule."
Since I assume this wasn't identified as a problem by the officials, they were never warned and would not be eligible to be DQ'd.