Feel for nodes... then look for them... then feel for them again. You will develop this feel as you go on in your training, if you are towards the start of it. The nodes in the scenarios you mention can be tiny and we all find this challenging.
Post-fixation in a clarifying solution (people use half formalin, half alcohol or things of that nature) is frowned upon at my institution because some attendings believe that our immunostains have not been validated for this... never mind that you would almost never order immunos in this scenario (maybe a keratin), or that a node examined on H&E is much better than no node at all.
But what I really wanted to say is that the patient's head will not explode if you do not find ___ number of nodes. Your attending's head might, but they need to read what the AJCC says:
"The ongoing confusion regarding the use of the lymph node guidelines is manifest by the increased association of the X suffix along with the N category when the optimal number of lymph nodes has not been assessed. Clinicians have been reticent to assign the pN0 designation, because the lymph node count has not reached a prescribed benchmark. Both the UICC and AJCC staging references, as well as subsequent editorials, have stressed that the pN0 designation, which indicates an absence of malignant cells in the extirpated lymph node basin, can be rendered appropriately even though fewer than the optimal numbers of lymph nodes have been assessed... Accurate reporting of the number of lymph nodes removed and pathologically analyzed is mandatory and should be used as a quality indicator for both the surgeon and the pathologist. Appropriate assignation of the stage group, however, depends on the appropriate use of pN0 and not pNX. The designation pNX is appropriate only if no lymph nodes are resected or examined."
This is from
http://www.cancerstaging.org/staging/PDFs/use_abuse_of_x.pdf, a useful article that also discusses the pathologist's other favorite staging term... "pMX".
So go ahead and look diligently, put in twenty cassettes of fat (our default maneuver where I work), but if you don't find twelve nodes, the patient can still be pN0.