I was hoping somebody could please advise me if I have an issue here.

Our armstrong engineered flooring was just delivered and I measured a 12-13 percent moisture content. Our subfloor is at 10 percent. I wasn't expecting the flooring to arrive with such a high moisture content. Is this a problem or would there be distortion issues during acclimation as it shtinks. Or this more of a concern with solid hardwood? Armstrong states the engineered flooring doesn't need acclimation so maybe it is not a problem.

Thank you in advance for any input or advice that you guys can offer!

Where are your located?
With a sub-floor at that moisture content your flooring should be fine.
The main issue is what the humidity is throughout the year.

We're in Chicago land.

Technically I am complying with armstrong requirements (subfloor 13 or less and flooring within 4 percent).

Do you know why Armstrong says acclimation is not required for engineered?

Thsnks!

We should be able to keep RH between 35-55 most of the year.

Armstrong provides the flooring in the right condition to stay dimensionally stable at the required conditions for delivery.
Engineered flooring resists expansion and contraction because of the way it is made.

Many manufacturers say that and it's not true. They say it so retailers can sell it and have it installed faster to reduce downtime. No one even mills wood at 12 to 13 percent to my knowledge.
Which meter are you using?

9% is the maximum the NWFA advises! Because you are in Chicago and will have much lower RH when heating cold air in the wintertime you can expect gaping particulary more so the longer the boards. And the stress of going from 13% to probably 8% will most likely cause distortion and possible delamination. Personally I would have someone take the MC of the wood and subfloor contact Armstrong technical services get the person's name and document their ok to proceed. CYA