So I've been reading these forums for a few months, and some posts are about the Macy's AMEX, and how it becomes a new tradeline added onto the credit report (one for Macy's regular store card, one for Macy's AMEX).
I assumed that just meant you would have both the store card and the AMEX as completely separate CCs, or that the store card portion would be inactivated once you have the AMEX, yet the line would still report for whatever funky reason until you close both accounts
However, reading a recent post, it seems that if you receive the AMEX version from the get-go (or maybe if you are upgraded from the store to AMEX), one card serves the function of both lines.
The way i'm interpreting it is:
You have a $1500 Macy's limit, but a $4,000 Macy's AMEX limit. While shopping in Macy's, you make a $200 purchase using your Macy's AMEX, yet it goes through on the Macy's store line, thereby making the available credit on the Macy's side $1300. However, you decide to make a purchase at Bloomie's using the same card for $500, and make the available credit on the Macy's AMEX side $3500.
Does this sound correct? In a way now, it doesn't make sense to me, because what happens if using the conditions above, you wanted to make a $3000 purchase at Macy's? What side does it go on, if any? Maybe you can chose what line you wish for it to go on?
Any help and clarification would be much appreciated 
@gen-specific wrote:I too recently discovered the twilight zone that is the Macy's Card. I got approved for a paltry $800 in store when I applied.
When I got my credit report from my monitoring service a few months later, I saw the $800 macy's card and a mystery AMEX card with a $3000 credit limit, I THOUGHT I HAD BEEN THE VICTIM OF IDENTITY THEFT
A quick google of the ID number showed me it was part of the Macy's card.
Online in my macy's account, it is clear that there are two credit lines, but for all intents and purposes you would think they would both have an $800 credit limit, because nowhere does it say what your limit is and they told me $800 in store.
Here is how it works:
1) exactly like you said.
2) inside macy's you can float balances only on the Macy's credit line. This doesn't touch your AMEX balance.
3) outside of macy's you can only float balances on your AMEX line. This doesn't touch the Macy's credit line.
its all on one card, branded as AMEX.
Weird huh!
I got soft CLI's on both. Currently 2400 on the Macy's line and 5000 on the AMEX line
Ridiculously strange, if you ask me! You'd think they'd want you to have an higher limit on your Macy's side than your AMEX side in that case! Oh well, that's their prerogative 
@daybreakgonesXe wrote:
@gen-specific wrote:I too recently discovered the twilight zone that is the Macy's Card. I got approved for a paltry $800 in store when I applied.
When I got my credit report from my monitoring service a few months later, I saw the $800 macy's card and a mystery AMEX card with a $3000 credit limit, I THOUGHT I HAD BEEN THE VICTIM OF IDENTITY THEFT
A quick google of the ID number showed me it was part of the Macy's card.
Online in my macy's account, it is clear that there are two credit lines, but for all intents and purposes you would think they would both have an $800 credit limit, because nowhere does it say what your limit is and they told me $800 in store.
Here is how it works:
1) exactly like you said.
2) inside macy's you can float balances only on the Macy's credit line. This doesn't touch your AMEX balance.
3) outside of macy's you can only float balances on your AMEX line. This doesn't touch the Macy's credit line.
its all on one card, branded as AMEX.
Weird huh!
I got soft CLI's on both. Currently 2400 on the Macy's line and 5000 on the AMEX line
Ridiculously strange, if you ask me! You'd think they'd want you to have an higher limit on your Macy's side than your AMEX side in that case! Oh well, that's their prerogative
That is what I thought as well daybreak, but my sister was approved for an $800 macys card, and a $6000 macy's amex. It confused me greatly.
Damn, what is with all these thread resurrections. I didn't even notice.