Shaykh Muhammad Bazmool said:
Oftentimes a person may say, "The Messenger ﷺ determined that Allah's names are restricted to 99. He ﷺ said, 'Undoubtedly to Allah belongs 99 names whoever enumerates them enters paradise.'"
I say: No! This narration does not promote restricting Allah's names; it only means that from the abundance of Allah's names there are 99. Whoever enumerates them enters paradise.
So, 99 is not the amount of Allah's names. The statement of Allah's Messenger is only with respect to enumerating that amount from His names. For him (he who does this) is this specification (i.e. the reward mentioned). Whoever enumerates them enters paradise. Outside of that, Allah's names are not restricted.