Question: Once D1 Schools have verbally committed positions 1-2 years in advance, do they continue looking at prospects from those same years in case they might find better players?
Answer: In general, if a D-I school gets a verbal commitment from a player, it can be assumed by both parties that this commitment will stand. Coaches will usually not keep looking to find a better player for that position. But they will often closely monitor the progress of the player who has committed, and if they feel she is not developing the way they expect her to, it's always possible the offer might be withdrawn.
A team's needs can change as well, and so a coach who thinks she's done recruiting, may find she needs to go out and replace a player who has left unexpectedly or who's been injured. And coaches at bigger D1 programs will sometimes continue to fill walk-on spots as they see their needs evolving specifically for a given year.
It's always smart to remember that recruiting is a fluid process, and a team's needs may change. So, while a coach believes that a verbal is indeed a commitment given by her and accepted from the player, until the student either signs a letter of intent or is confirmed as a member of the team, things can---and sometimes do---change! I hope this helps.