That's a very good point. Sam's achievement shouldn't be understated, as he is the first and last mention of any harm coming to Shelob. Beren did pass through Shelob's birthplace in the first age as he traveled through Ered Gorgoroth (he was the only one of the children of Ilúvatar to do so), and I wonder if he crossed paths with her, as she was the final and mightiest of Ungoliant's spawn and therefore must have had a place of dominance amongst the other great spiders there.

Imagine being a creature born of an ever yawning abyss, living for eons; and possibly the second mortal to evade your maw is not Beren, greatest of men, but rather Samwise, the humblest of the children of Ilúvatar, and not only did he evade her grasp, he wounded her and stole her finest meal in what was probably hundreds of years. Sam was truly one of the most valiant souls to ever walk Arda