Does the US Consulate know visa overstays?

The US Consulate has access to all kinds of databases that we do not know about.

Do they know overstays?

They can find out if suspicious and they check. Obviously people have been issued with visas in error despite previously overstaying and having a ban. Many times those people are apprehended by immigration at the port of entry.

but not quite sure if I have overstayed previous visa since I had D/S.

D/S non-immigrants can overstay although they do not start accumulating unlawful presence.

Nonimmigrants Admitted for Duration of Status (D/S). If USCIS finds a nonimmigrant status violation while adjudicating a request for an immigration benefit, unlawful presence will begin to accrue on the day after the request is denied. Similarly, if an immigration judge makes a determination of nonimmigrant status violation in exclusion, deportation or removal proceedings, unlawful presence begins to accrue the day after the immigration judge’s order or the day after the Form I-94 expired, whichever comes first. Note that accrual of unlawful presence does not begin on the date that a status violation occurs, nor does it begin on the day on which removal proceedings are initiated.

So basically if in your case USCIS did not find an immigration violation or you never went before an immigration judge, you did not accrue unlawful presence. However student with D/S are supposed to leave within a set number of days of grace period.You could be stopped and denied entry at the port of entry if the immigration officer determines this.

If you are an F-1 student and have withdrawn from classes after receiving authorization from ISSS, you have 15 days to leave the U.S.

If you have withdrawn from classes without previous authorization, you have no grace period and must leave the U.S. immediately.

If you are an F-1 student and have completed your program of study, you have 60 days to leave the United States, apply for change of status, or transfer to another school. Note that this does NOT apply if you do not complete your program; if you leave without graduating, you do not receive a grace period.

If you are a J-1 student and have completed your program objective, you have 30 days to leave the United States or change to another visa status. Note that this does NOT apply if you do not complete your program objective; if you leave without completing your program objective, you do not receive a grace period.

Revision 8/8/2018

U.S. Citizenship and Immigration Services (USCIS) today posted a policy memorandum (PDF, 179 KB)changing how the agency will calculate unlawful presence for students and exchange visitors in F, J, and M nonimmigrant status, including F-2, J-2, or M-2 dependents, who fail to maintain their status in the United States.

The day after they no longer pursue the course of study or the authorized activity, or the day after they engage in an unauthorized activity;