How can I count blocks in a large build?

I use frequently the World Edit command //count but I noticed some weird things.
When I do //count grass in a selection zone which is a straight line of 472 blocks when I'm placed at the end of the line, it returns me "162 blocks".
That led me to think that it was due to loaded/unloaded chunks server side, because I know the server side chunk limitation is 10 chunks, and 10 * 16 = 160 which is close to 162 (the two additionnal blocks could have been in front of me). But if it's impossible to have all the chunks which contains my build loaded (if it's 472 x 259 x 254), and //count only affect the loaded chunks (as well as copy, stack, and a few other ones), how can I count how many blocks is my build?
I know it's not really important but I just wanted to know if there was a way to count blocks despite the chunk limit.
Thanks in advance!

 

Yeah, that's quite annoying, the unloaded chunks are replaced with only air, so it deletes what was already there when you do //stack or //copy-paste

 

If I stand in the middle, I count already half a million blocks, as I said, the build is massive and it will surely crash the server if I replace all the blocks

The command distr is very usefull, but way slower than count. To select my whole build, the smallest selection possible is 31 millions blocks (literally half the avaliable space), the command distr will have to count all of them which will take a very long time, and as NickManEA said, it probably won't work too.

 

I just tried to do that, yeah, but there's apparently a limit of modifying chunks, and I have to enter the command like three time for each type of block to replace them all.
It's not perfect, but it works. Thank you!

Edit: There's no proper "limit of modifying chunks", it's just that the command //replace seem to only affect loaded chunks