Update and storage space requirement confusion

[clayto]

I have read various contradictory items about the MS recent statements concerning the related topics of minimum storage space requirements for (the 'May") feature update; and Reserve Storage. My favourite magazine, Computer Active, had to print a correction / clarification but it still leaves me confused. It is of particular concern to those of us with 'small storage' devices such as 2-in-1 Tablet PCs. 

In particular I am no longer sure about the temporary use of external devices such as USB flash drives to assist updating. When it was announced a while back that this was possible ----and I found it to be so --- I was relived. It seemed to solve the storage problem. But there has been no mention of it in recent articles and statements. I was pleased to discover that when the October update arrived (in February) it had actually used my integral SD card in the process, which seemed a logical improvement, but I have not seen this mentioned anywhere. 

This is of concern to me now especially, as a few weeks back 7 GB of my small storage vanished and for a while I assumed that the Reserve had been installed. On learning this was not so I realised I do not have sufficient free storage if external drives cannot be used.