Yes, sometimes series can sell out in a short span of time. Take for instance, http://www.neonmob.com/series/hottest-summer-ever (sold out in a day) and http://www.neonmob.com/series/chibi-heroes (sold out in a few days). However, the Orphanage series is not one of those series.
I’m surprised though, when I was collecting it a while back (I think November) free packs were still in abundance. I never even knew it ran out of free packs until it sold out! I never knew such a large series to sell out so fast.