I think that there is a time during search that everyone feels like their search is difficult. What I am going to write about is meant more for those who have been searching for a period of years or even decades. The information contained here is in RARE cases and is more than likely NOT the case if you have been searching for someone for a few months.
Some of what I write may be applicable in one state and not in another. The state specific search and support groups will be able to guide you in regards to your specific state.

It is rare that an adoption agency changed the details of the birth such as date of birth or place of birth. The date of birth will rarely be changed by as much as a year except when a child was much older at adoption. The purpose was to try and make a search impossible.

Changing this information was considered deceptive practice in most states. However, there have been clerical errors meaning a typo was made and the date of birth was off by a few days, rarely more than month. If an infant adoption, it is extremely rate for the date of birth to be off by more than a month. Telling a adoptive parents that a one month old is a three month old would make the adoptive parents question the size and development of the infant. I have never experienced adoptive parents being in cahoots with an agency to change the date of birth.

If you find someone that fits the information for the person you are looking for but the dates and places don’t quite match, you can have a DNA test done. This does cost money and it can be pricey and I would say that you need to have convincing proof that you have the right person.
If you live in a state that has open records, send for your original birth certificate. If you live in a state that does not have open records, you are left with using the International Soundex Reunion Registry (ISRR), internet bulletin boards, state specific registries, the agency who handling the adoption, and petitioning the courts. When searching the registries look for not only your exact date of birth but dig to find out if the date of birth and place of birth was changed. Use an approximate date to find someone.

You want to do as much detective work as you can and search every public record available. Look beyond the dates that you think relate to you to see if there may be something for you on another date.

Again, these circumstances are rare but do happen. By searching beyond the dates that you think relate to you, you may be able to find someone that is searching within about six months of when you think your birth occurred and if other things match, you may have found the person you are searching for. I would explain the situation to the person and ask about genetic traits. If you have matching traits you may have a lead. When I say trait I mean not only physical characteristics but also things like hobbies, careers, and personality. I then suggest exchanging photos. If you feel that this is worth pursing when reviewing the photos you want to look for obvious similarities like eye and hair color and other things like ears, nose, mouth, jaw, and chin shapes, an bone structure. Try covering a part of the picture and concentrate on one feature at a time and it is possible that not all features will match because they could be inherited from the other birth parent.

If you see similarities you may want to discuss medical problems such as vision, teeth, hearing, heart, spinal, and mental disease. You may also want to consider your blood types.

Next, discuss whether the circumstances surround the adoption and see if there are similarities. If there are any discrepancies that agencies, courts, lawyers or intermediaries that could change, ignore them.
If you think that you have a match, consider a DNA test. Depending on the circumstances the prices are $300 per person and up. First though, be sure that you have exhausted all other possibilities so that you have solid reason to believe that the DBA test will prove to be a match.

If you haven’t found the person you are searching for and have exhausted all other possibilities, you may want to consider checking out homeless shelters or drug rehabilitation programs. Folks in these types of situations are difficult to locate because there are no records on them. The rarely have a car so they don’t have a driver’s license. You won’t find them on voter’s registration lists and can basically can be impossible to find except for the programs run by the cities they may be in.

Another thought is that for the searchers that involve older persons. You may want to consider looking at nursing homes. Residents of nursing homes do not show up on a database search and are not listed in the phone book or in online directories.