Your wallet is an endless series of addresses. But Armory don't generate them all (it can't, of course). When Armory has generated 1000 addresses(*) without any coins in them, it assumes that it has seen all addresses and stop generating new ones.
This isn't exactly true. There is no real sense of an ongoing lookup in Armory. You are implying Armory would keep on generating addresses on the wallet's chain as long as the last 100 aren't empty, which isn't the case. When you create a wallet, Armory pre-computes the first 100 entries on the chain. When you restore from a root key, it pre-computes 1000. When you restore a digital backup, it doesn't extend the existing chain at all.
To understand this you have to consider the engineering perspective:
In order to check an address balance you need to know at least its relevant utxos. However this information alone is not enough. You could very well have a wallet with 100 empty addresses (that have a transaction history) and the 101st address with an actual balance. If you only scan for balance, you would miss that 101st address. The criteria therefor is not balance, but transaction history.
There is no true shortcut to look that up. You have to parse the blockchain for that data one way or another. In case of lite wallets, they rely on a supernode server that tracks all blockchain history, therefor such incremental lookup scheme is possible (at the cost of your privacy). For full node wallet (i.e. that process their own blockchain data), you have to run your own supernode to support this feature (at a huge resource cost compared to the average individual use case). Scanning packs of 100 addresses sequentially is not a reliable approach, each scan is essentially as expensive as the previous one.
Armory side steps the issue entirely. There is a default, fixed lookup, and it is left to the user to manually increase that lookup if they think it necessary. Armory is an advance wallet after all, we expect our users to understand this engineering limitation and fill the gap thanks to their own expertize.