There could be something in that.
During the 80s I subscribed to Murder Casebook which was about 150 issues and then I would also need the folders to put them in.
Even though it was ordered every week there were 3 issues I couldn't get and 30 of my issues stayed out of folders because they had run out and weren't making anymore.
This also happened in the late 60s/early 70s with an Encyclopaedia Magazine that my Grandparents bought for me and that was never completed.
Every time I look at these type of mags I just think that people will get ripped off.
I can't speak for other minor companies, but De'Agostini has thousands of happy builders who have been looked after well by them.
The horror story's regarding incomplete series form DA stem from confusion, in that ALL partwork company's have to 'Test' series to gauge if there is enough interest to run a full series, ultimately there has to be a minimum number to make a series viable to run its full course.
Tests generally run for 4-6 issues in selected areas of the UK. When the test is complete, any buyers can obtain a full refund for the issues purchased.
Once the the results are known, a decison is then taken to progress the test to a full run or not, and if successful, generally a series will then appear as a full run approx 6-12 months after its test, as a TV advertised item, by which time tweaks may also have been made to the series to improve its content based on what the test customers thought of the initial issues seen.
Sadly its the nature of the beast that testing has to be done, but it has to be done to gauge potential and that the item will not turn out a financial loss.
Generally if you see a TV advertised item, then it is not a series test, simply because TV advertising is very expensive, and therefore would not be done for an item where its future roll out is uncertain.
So basically, if it's from DA and it's on TV, you will get the lot.
And believe me, ship building is so therapeutic it's untrue. I fond plastic models annoying and not worth it, but full wood models have numerous tasks such as planking the hull and sanding it smooth which are a delight to do. Unfortunately as I said earlier, the instructions in advanced ready made kits are normally inadequate and people get frustrated too easily and give up, leaving a half built model and spent cash.
In partworks, much attention is made to the instructions to make it as easy as possible to complete the model, making it a far more enjoyable experience. You also get a to read about the history of what you are building, which, if you are a maritime buff like myself, will find immensely enjoyable.
Also, a common trap of getting all the bits at once often leads to rushing and mistakes, which in a wood model, cannot easily be corrected. Getting a few parts each week means that more time can be taken, usually ending in a far more satisfying result.