While searching for the metes and bounds of my lot, I have learned the following details regarding the process for getting deeds, plats, and other documents from the county online resources. Sadly, these processes don't seem to apply to my case.
This is a nice top-level page that wasn't really a whole lot of help (it led back to the circuit court page that I'd found by other means):
http://publicrecords.onlinesearches.com/Maryland-Land-Records-and-Deeds.htm
This is the web page for the land records office of the county circuit court:
http://www.courts.state.md.us/clerks/howard/landrecords.html
I called the phone number for the land records office, and the person there told me the URL for the Maryland Land Records web site.
http://www.mdlandrec.net
It requires registration for user account, but the process was not difficult, and once I got in I found this site to be an easy to use well indexed archive of pdf scans of record books and pages (by liber and folio). The faq advised to go to the old reliable property tax record page (SDAT), on which all I have to do is enter the address and I get the sales history, deed numbers, and other information.
http://sdatcert3.resiusa.org/rp_rewrite/.
Unfortunately, none of the deeds listed on my property tax record had the metes and bounds, and the plat reference in the tax record was blank. The deeds, going back several years, all referenced one particular plat by liber and folio. Plugging in that reference (including the alphabetic three character prefix) returned a scan, but it was of a hand-written note saying "see plat book..." with a number that does not follow the usual format and did not come up on a search. Interestingly, it mentions another document as the reason for the move, a document which had yet a different three character prefix (these prefixes are the county clerk's initials. The books are all indexed by clerk's initials and number, but fortunately the clerk's initials don't seem to be important for accessing scans with the online tool. This generally implies that the books are numbered continuously regardless of the clerk). I found that the resolution document could be found on mdlandrec.net; it's a record of a zoning decision. It seems that a subdivide somewhere else in the neighborhood, a long time ago, caused the plat to be revised, and consequently my plat was pulled from the location referenced by all deeds before and after and stuck in this mystical other book.
Through some method of blundering that I haven't figured out yet how I've accomplished, I can get to a plat archive at the following link. It responds to the number and page given for the mystical book, but it was listed as not scanned.
http://plato.mdarchives.state.md.us/msa/stagser/s1500/s1529/cfm/dsp_court.cfm?county=HO
Clicking on the "Accession number" got a simlarly empty listing, and clicking on the link from that listing got a request for an account and password. It turns out that the original (not new) plat reference produces a scanned listing. Furthermore, a guest password for the plat archives (user plato, pw plato#) has been provided, as described in this user's guide:
http://plato.mdarchives.state.md.us/msa/stagser/s1500/s1529/cfm/faq.html
