Those are great questions.
Height- can be variable and very subjective. The question usually is when the person was last officially measured and how accurate that is. Even measurements at doctors offices or schools can be off if the device is not calibrated correctly. Many of our missing teens might not have accurate records. In cases of neglect or abuse (reasons to run away) I am certain routine visits to doctors for wellness didn't occur most of the time. Usually, the only time a teen has routine contact with a clinic will be their 12 year-old Measles-Mumps-Reubella vaccine needed as a booster. So many records will list that last contact status as record. As we all know, teens can grow well into their 20's at times. This can lead to an under-estimate in height.
In long ago cases, people often rely on their memories (can be biased). If siblings are younger, they might remember someone as a lot taller due to idolization. If an environment was hostile, children/family members can percieve those who hurt them or those who protect them as larger than it is true. In families where there is dissonance and struggle, people often are not overly focused on those details. If a sibling or child who comes and goes often, people will guess their height based on a person with shoes on because that is their only reference. We often rely on what people say when they are asked how tall they are as well. How many of us "over-state" how tall we are on our DL's?
Another reason it can be off is post-mortum changes. Bodies can elongate after death as the muscles relax. They are not "taller" but our muscles and tendons serve to "hold" our joints together for body mechanics. Once those are relaxed, people can be taller. When we stand on a scale, gravity can "compress" us. When we are measured head to toe, on our backs, we can be taller due to anatomical positioning. Especially if our muscle relax.
Pollen-We have no idea where she got the jacket and clothing. The jacket was given to her most likely as it was ill-fitting. It could have had the pollen on it when she got it causing cross-contamination as she wore it. With the California connection, I would surmise more that Tammy was not in California, but the pollen came from the truck/car she was in for a week, etc. Tammy could have easily "lifted" the jacket from a truck stop as well if she was cold. IMOO