That hasn't been my experience. They seem to claim every terrorist attack that happens as their ow.
More about how and why ISIS does not normally and randomly claim responsibility for mass killings.
“The vast majority of the Islamic State’s claimed attacks were undertaken by men acting in its name, often after leaving short video statements confirming their intentions.
“A false claim of credit in Las Vegas will effectively shred the Islamic State’s news agency’s credibility. It will become a news agency that was once reliable, and now associates itself indiscriminately with heavily armed crazy people in casinos. I see little advantage in such a shift. When Amaq claims an attack, it makes itself hostage to the facts that are revealed in the follow-up investigation.”
https://www.theatlantic.com/international/archive/2017/10/isis-amaq-las-vegas/541746/