Unfortunately, the term "inverter duty" is part of the snake oil that flows abundantly in the drive-motor field. Each manufacturer defines it differently with some on the low end calling any motor with Class F insulation "inverter duty" or maybe "inverter ready". On the high end are those manufacturers that will only put that title on motors that have either an auxiliary blower or are rated full torque down to stall by virtue of oversized framing or a TENV enclosure.
A couple of things can be said without qualification, tho. First, inverter duty ratings as far as insulation is concerned are only a factor in 380VAC and higher applications. Second, in those higher voltage applications, an insulation class A or B motor is NEVER good enough. Under the best of conditions, motor life is measured in days and weeks, not months and years. Class F insulation, at the least, is required.
Further, heat management issues in motors are really a separate consideration from insulation integrity issues. There are many applications where Open Drip Protected or Total Enclosed Fan Cooled motors are plenty good enough even at low speeds. You must understand how the load uses torque over the speed range and how that compares to the manufacturers' motor heat dissapation curves to be confident you've got it right without over-specifying.
And don't forget about ambient temperatures. A motor operating in a cold storage warehouse will likely be able to work harder than the same motor located next to a furnace or other heat source.
Unfortunately, the subject of long motor lead lengths, reflected waves, etc. is being muddied by more snake oil. If you talk to reactor manufacturers, any motor with leads over 50 feet in length is sure to fail while some drive manufacturers state clearly in their manuals that at least 250 feet lead length is OK without the addition of extra hardware. My own experience is that problems with reflected waves and especially electrical noise (another ugly subject full of snake oil and false claims) are highly unpredictable. I've seen problems on short leads and no problems on long leads. I hate to admit it but, most of the time, I'm baffled! I try to write my quotations in such a way that I can work as a partner with my customer to solve any problems that come up, rather than as an antagonist. That way, I can quote the simplest system that will likely do the job and, if there are problems, we'll deal with them as efficiently as reasonable people can. Usually, but not always, that works out quite well.