Here's the problem: all cases in Maryland are public records and can be either accessed directly at the court house by review of docket records and case files, or reviewed on-line on the Maryland Judiciary Case Search system. Until those records are expunged and all the files, docket entries, on-line data, and CJIS/NCIC data erased, any private entity can access those records and create their own private database. When the expungement goes through, it only applies to official government data bases. The private entities which may have downloaded or recorded the info would not be reached. That's the only risk. However, I am aware of no entities which have the financial wherewithal to vacuum up all that data and archive it. Those entities only make money when someone, like an employer, comes to them and pays them to do a background check on a specific person. That's when they start looking at all the available databases for a particular individual, and if the case has already been expunged, they won't find it. But in this brave new world, who knows who has already researched your background information a decade or so ago and still has it in their files, for no particular reason? Used to be only the FBI, but you already know about the three main credit bureaus and all the data they have on you. Civil court judgments have been recorded by these private entities for decades before the internet, on everybody even though there were no inquiries about those people before they obtained the data. Criminal offenses as well? Don't know the answer to that one, but if there's a profit in it, somebody is doing it.
Expungement applies to the information that the government has. A private company that has gotten your information is not necessarily obliged to remove it.
The arrest record is a public record, and once a private company owns it, you would have to get them to remove it. That can be impossible to achieve. For example, if your arrest was in the local newspaper, how could you take that information away from me, if I still have a copy of the newspaper? The upshot is that you can expunge the record, but that does not mean that all traces of it are gone. That's the bad news.
The good news is that an arrest is not a conviction. Without knowing what you were arrested for, it is hard to be more helpful.