SCCM distribute software computer out of collection get it

Hi,

Thanks for reading my question.

I have distribute one software to 18 PCs with one new collection which has no any rule.

I manually input 18PC names in it and begin to distribute.

But after a while serveral(around 5PC) PC which didn't in this collection got my package.

I have checked my new collection many times and only 18 PCs in it and no rule.

Anyone could help on this issue?

Thanks in advance.

Rowen