Igf1 And Gh

i know that an increase in IGF1 is the main cause of muscle gains while using GH thats why many use IGF1 instead of GH as it is a cheaper alternative. I know most people run igf1 for a period of 28 days or so as IGF receptors in muscle down regulate quickly and the igf1 ceases to be effective until you take a break.
My question is considering that most people use GH long term eg nine months would you noy cease to make any gains in muscle mass after the first month or so, or is their something else that GH does to the bodt to cause further muscle gains.