Overprint GANDHI stamps

I was thinking that this overprint Gandhi stamps were error (knowing or unknowing) but I was not sure at all. Recently I came to know about J & H Stolow Inc. ( Julius and Henry Stolow).

This company was world largest stamp wholesaler until 1970. You can read more about them at wikipedia link which is http://en.wikipedia.org/wiki/Henry_Stolow

Following are some of the Overprint stamps of Gandhi.

There are 2-3 more of this kind of stamp from this 2 countries.

After reading about J & H Stolow Inc and doing more research I found out that
1) They were preparing stamp for Africa and other smaller countries.
2) They did overprinting of stamps
3) And lot more.................

One of their overprinting link is following http://www.stampnotes.com/Today_in_Postal_History/033156.html

Now after reading this link and also about the J & H Stolow I am curious about Gandhi overprint stamps from Cameroun & Nigragua which are currently selling from some european countries where this J & H Stolow has some roots.

Until now I was thinking it is good item to collect after reading from different sources but now I am confused after my own research.

Also I am not sure what is the real value?

If someone has any more info than please add in comments or let me know so I can update this and provide more information to current as well as future new Gandhi collectors.

Thanks

Note:-

I think this is anothe example of making money using Gandhi. This stamps are selling currently on ebay.com for 30-50 dollars and on ebay.in (India) it is selling for enormous amount which is some where from 2000-10000 rupees which is ($40 -$200)