1♣ was alerted, asked, and described as short, showing 2+ clubs, playing 5-card majors. 3♣ was not alerted. 4♠ made.
After the hand N/S realised East had bid 3♠ on a minimum, and discovered 3♣ was natural and forcing. They claimed it should have been alerted, and North said he would have bid 4♥ not 3♥ if he had known 3♣ was forcing - and now the spade fit might be missed.
The sequence is not specifically covered in any of the examples in the regulations. The basic regulation says:
EBU Orange book 5E1 said:
Unless it is announceable (see 5 C and 5 D), a pass or bid must be alerted if
{a} it is not natural; or
{b} it is natural but has a potentially unexpected meaning.
So is a forcing 3♣ 'potentially unexpected'?
If there is MI, is there damage?
If so, how do you adjust?

Help

------P--1♣-2♥
-3♣-3♥-3♠--P
-4♠--P---P---P