The shelf was alerted, there was certainly a pile of clothes on it that night, so why weren't a few of those clothes alerted at the gym?
There is a black item at the bottom of the pile in the wardrobe, immediately underneath Sean's red T-shirt. I believe that black item is a top belonging to Kate, which can be seen displayed on the VRD video in the same inspection batch as the 2 rucksacks and being tossed around by Keela.
What is clear (if you believe the testimony of DP) is that the red T-shirt was not being worn by any of the children at the time of his brief visit after 6.30pm, as they were all in their pyjamas, alive & ready for bed. We do not know what Kate was wearing between 6.30 & 8.30, after which time she went out in jeans.
As you rightly pointed out previously, there was insufficient post-mortem time for cadaverine to have developed & been deposited on any of the marked clothing before the parents left the apartment, had anything happened to Madeleine in the interim.
So, if the clothing wasn't contaminated at that stage, what was Eddie really alerting to?