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When it comes to Tesla and firmware updates, there is no such thing as "typical". Yes, updates prior to Model 3 deliveries were more frequent, but have since slowed relative to the frequency of what a Model 3 owner will see.
Your best bet to see if you are out of the norm is to use something like TeslaFi or ev-fw to gain a sense of how many similar models to yours are on your firmware version. There are often a few different firmware versions that are considered "current" at any given time for any one model/AP hardware/country.
18.50.6 was released on Jan 22. most people didn't get it till Feb 2. So you didn't really sit on it for 4 months. it's more like 2 months. which is typical.