BCC not sending to all in contact group WLM 2012

Until quite recently I had been able to send a group emailing out to 70 people using the undisclosed format with my contacts going in the bcc field so as to protect everyone's privacy.  This week I found out a majority of my contacts were not getting their emails, and I thought I had read that perhaps WLM was limiting the number of bcc's?  I tried sending a group email out using the regular to: line, and even though I used the "group", all of the emails appeared when it was received.  I would like to be able to go back to my "old way" of doing things, but I don't know if I can risk it.  In my "sent" mailbox it shows all the emails, but they just weren't received, because I checked with everyone on my contact list.  I have not gotten any error messages or bounce backs.  I am running Windows 7 and WLM 2012.  I did not upgrade using the patch that caused so much trouble a while back.  Does anyone know what is going on and if there is a solution to this?  I checked with my ISP and they do not place limits that would effect a group size of 70.