Johann and Elizabeth -- Immigration

I've been working to uncover as close as possible when Fred's parents moved to America. There are a few different documents to consult here. The first place considered was the naturalization records, which typically spell out the Date and port of arrival in the U.S. Johann's records show this occurred on April 11, 1871. However, whomever took these records was not the most thorough. His address is just listed as "Jamaica Plain" and the Date and port of arrival is listed as empty.

The 1900 US Census has a convenient Citizenship section, which includes an input for "Year of Immigration to the United States," followed by "Number of Years in the United States." There are inputs for Fred and Elizabeth in the census, both for the year 1852, and thus calculating against the 1900 date of the census, they'd spent 48 years in the United States.

This sets us pretty well in the year 1852, but I wondered if I could get any more specific. Prior to migration, Johann and Elizabeth had given birth to some children, and consulting their records (particular Jean Kohlhepp, who was born, baptized, and died in 1852) we can get a closer date.

Ancestry's collection of "Hesse, Germany, Lutheran Baptisms, Marriages, and Burials, 1661-1957" has 3 entries for Jean Kohlhepp born to a Johann Friedrich Kohlhepp and a Maria Elisabetha Benedicta Wetzler:

(a) General record of birth, baptism, death

Name: Jean Kohlhepp

Gender: Male
Birth Date: 11 Mrz 1852 (11 Mar 1852)
Baptism Date: 21 Mrz 1852 (21 Mar 1852)
Baptism Place: Evangelisch,Grossenlinden,Oberhessen,Hesse-Darmstadt
Death Date: 17 Jul 1852
Father: Johann Friedrich Kohlhepp
Mother: Maria Elisabetha Benedicta Wetzler
FHL Film Number: 269706

(b) Baptismal record

Name: Jean Kohlhepp

Gender: männlich (Male)
Event Type: Taufe (Baptism)
Birth Date: 11 Mrz 1852 (11 Mar 1852)
Baptism Date: 21 Mrz 1852 (21 Mar 1852)
Baptism Place: Hessen, Hessen (Hesse), Deutschland (Germany)
Father: Friedrich Kohlhepp
Mother: Maria Elisabetha Cramer [NOTE: Name from prior marriage]
Author: Evangelische Kirche Großen Linden (Kr. Gießen)
City or District: Großen Linden
Parish as it Appears: Großenlinden
Page Number: 16;17

(c) Burial record

Name: Jean Kohlhepp

Death Age: 4/12
Event Type: Beerdigung (Burial)
Birth Date: abt 1852
Death Date: 17 Jul 1852
Burial Date: 20 Jul 1852
Burial Place: Hessen, Hessen (Hesse), Deutschland (Germany)
Father: Johann Friedrich Kohlhepp
Mother: Maria Elisabetha Kohlhepp
Author: Evangelische Kirche Großen Linden (Kr. Gießen)
City or District: Großen Linden
Parish as it Appears: Großenlinden
Page Number: 12;13

Based on these records (I do not have the originals, it is a text only record database), they would have not left prior to Jean's burial in Grossenlinden on July 20, 1852. So the immigration occurred in the latter half of 1852. These records also cast further doubt on the Jewish heritage question; one could argue that one parent just accommodated the other in religious matters, but at the moment all we have is evidence of is a Lutheran background.

While this might seem to lock us into the 1852 date, there is some ambiguity in the records. The 1910 federal census, after Elizabeth passed away, still contains similar Citizenship information, and for Johann, this time it lists the year as 1856. Which is correct?

I'll need to find the specific records whether birth or marriage records documenting Amelia's birthplace, but the generic online records have her born in 1855 in Massachusetts, which would mean that Johann and Elizabeth migrated earlier.