@Lydia Lorraine does your client have an Architect? They should be able to tell them how much they can build by right and through board approvals. The BOZ is the Bethesda Overlay Zone which mainly governs the development of the Bethesda Downtown Plan as it relates to density, heights, affordable housing, parks, and design. The density has been capped at 32.4 million gross feet for development. Each project that is built in this district has to be subtracted from the 32.4 million gross feet. Here is a link from Montgomery County. There are a few ways to build more than what is allowed by right in BOZ.
1. Affordable housing will increase the FAR. The total affordable units are based on a percentage of the total units and they have to be disbursed equally throughout the building (they can't all be in the basement). Sometimes there is a minimum amount of units that are required but if additional units are built then more credit may be given.
2. An owner may also ask to exceed the FAR but is required to obtain approval from the board. If they ask this there should be a good reason and hopefully, other cases that have already been approved in the area with similar circumstances.
3. Another option is if an owner owns multiple lots. If one lot is used for the public such as a park or public art then the gross floor area for that property may be transferred to another property within the Bethesda Downton Plan.
As you can see there are many ways to get more than what is allowed by right. Most likely asking for more will add 4-10 months to the approval process as the board will have to approve it and I'm sure there is some back and forth between parties before an agreement is reached.
If you provide an address I can give you more detailed responses. If you have more questions feel free to contact me.
Good Luck.