Cross-checking information is important in determining the accuracy of a source because

Cross-checking information is important since it is one of the main methodological sources of validating knowledge in areas such as History, Law and Social sciences. Cross-checking is to History just as the scientific method to Physics. The claims and authenticity for example of some documents are validated through the use of this procedure.

The results of cross-checking information also occur in some settings where field research is carried. It can be used when engaging in anthropological or sociological research. An example of it is seen when interviews are carried in mental health institutions, to patients, to doctors, families, and surveys also are checked against people that are related to the object of study. These are corroborated with people who can help or provide unbiased knowledge on the inquiries.  See below ... :)

the berlin blockade was an international crisis that arose from an attempt by the soviet union, in 1948–49, to force the western allied powers (the united states, the united kingdom, and france) to abandon their post-world war ii jurisdictions in west berlin. in march 1948 the allied powers decided to unite their different occupation zones of germany into a single economic unit. in protest, the soviet representative withdrew from the allied control council. coincident with the introduction of a new deutsche mark in west berlin (as throughout west germany), which the soviets regarded as a violation of agreements with the allies, the soviet occupation forces in eastern germany began a blockade of all rail, road, and water communications between berlin and the west. on june 24 the soviets announced that the four-power administration of berlin had ceased and that the allies no longer had any rights there.

under god i have placed my chiest strentgh and the safe guard to my loyal subjects